California is one of only 11 states that don't require a booster shot for middle-schoolers. Efforts to require immunization for younger adolescents continue in the Legislature.

Public health officials say California's lackluster immunization rates could be a factor in the epidemic spread of whooping cough, a bacterial disease expected to take its largest toll in the state in five decades.

The state is the only one in the nation to report such a dramatic surge in pertussis, according to the U.S. Centers for Disease Control and Prevention. Five newborn babies in California have died so far this year, and at least 910 people are confirmed to have the illness.

Adolescents can play a major role in transmission of whooping cough; the bulk of pertussis cases in Marin County have been diagnosed in 5- to 17 year-olds. Located just north of San Francisco, Marin County, with a population of 250,000, has been one of the worst-hit counties statewide, recording 187 cases — more cases than in the past 10 years combined. Los Angeles County, with a population of 10 million, has recorded 148 suspected cases so far this year.

Efforts to require the whooping cough shot in adolescents have stalled in the California Legislature in recent years because of the budget crisis. Support has been widespread in the Assembly, but the bill has failed to win support in the Senate appropriations committee.

One concern is that California would have to pay hundreds of thousands of dollars for vaccinations for children on Medi-Cal, the government insurance program for the poor, said Assemblyman Juan Arambula (unaffiliated- Fresno), who has been trying to require the shot since early 2008.

"Sometimes we can be penny-wise but pound-foolish," said Arambula. He said the cost of immunizations would be less than the state's future cost of paying infected children's hospital bills.

Dr. Robert Benjamin, deputy health officer for the Alameda County Public Health Department, said the whooping cough epidemic should cause parents to reexamine their decision to skip or delay recommended vaccinations.

"Anyone who has experienced pertussis, either themselves or in their kids, they know this is not a disease to mess with," Benjamin said. "This is a disease that can kill the most vulnerable newborns — not only in their households, but in the households of other people."